This is a request for a time-of-flight (TOF) mass spectrometer. The instrument will play a pivotal role in the research projects of many investigators at the Salk Institute and researchers at other academic institutions (see letters of support). We will obtain accurate mass and structural information on novel hormones, toxins, and growth factors and characterize the sites and nature of post-translational modifications in molecules of known primary structure. A group of 10 investigators has been identified whose research is dependent on analyses only possible with the requested instrument. The sensitivity of the instrument is essential to our current attempts to characterize novel peptides and proteins. Results obtained on a variety of unstable peptides illustrate the increased sensitivity available with pulsed ion extraction and the laser optics on the requested instrument compared with continuous extraction and the more rudimentary analysis currently available. The instrument will also be vital for identifying the site of phosphorylation in phosphoproteins where either the low level of phosphorylation or the deleterious effects of introducing a radioactive tracer prohibit conventional electrophoresis and radioactive chemical sequencing protocols. By analyzing the hydrolyzed phosphoprotein, we will increase the sensitivity of intact mass analysis while the use of fully automated precursor selection and PSD will allow rapid MS2 analysis of the phosphopeptide to help identify the site of phosphorylation when more than one potential site of phosphorylation exists in the peptide. The mass accuracy and resolution available with the upgraded instrument will be extremely valuable for the identification of hydrolysis fragments generated from 'unknown' proteins. The instrument will be amenable to a proposed approach of measuring a peptide both prior to and after carrying out reduction and thereby enabling PSD analysis of disulfide bridge-containing peptides. Other instruments already available at the Salk Institute include a double focusing magnetic sector mass spectrometer with both liquid secondary ionization and laser desorption ionization sources, an electrospray ion trap mass spectrometer, and gas phase sequencers with PTH analyzers. The requested upgraded TOF mass spectrometer is needed to complement the strong classical Edman sequencing approach at the Salk Institute. The instrument will be located in the MS Facility. A significant institutional commitment will ensure that this instrument is operated and maintained by trained personnel. All measurements will be made under the supervision of A. Craig.